1. Field of the Invention
This invention generally relates to data processing systems and more specifically to a data storage facility for use with in such data processing systems that has the capacity for replicating data for independent access and for periodically updating the data from a standard.
2. Description of Related Art
The above-identified U.S. Pat. No. 6,101,497 discloses a method and apparatus for replicating data for various purposes, all with minimum interruption to normal data processing activities. In one specific implementation, a data storage facility uses a business continuation volume (BCV) concept. Under this concept an ESTABLISH command from a host to a disk storage facility with a BCV capability effects a relationship between a first logical volume (hereinafter a xe2x80x9cstandard volumexe2x80x9d) and a second logical volume (hereinafter a xe2x80x9cBCV volumexe2x80x9d). The storage facility copies data from the standard volume to the BCV volume in a orderly fashion and transparently to any host applications. That is, a host application or program can continue to communicate normally with the standard volume using conventional I/O requests even as data is being copied from the standard volume to a BCV volume.
When the BCV volume has an exact copy of the data from the standard volume, the BCV volume is xe2x80x9csynchronizedxe2x80x9d and the data has been replicated. Once synchronized, a SPLIT command can separate the BCV volume for other uses independently of the activity between the standard volume and its host applications. Specifically, the BCV volume can interact with an other application program, such as a development program under test or a backup program, without any danger of corrupting any data on the standard volume. During these independent operations the application associated with the standard volume can alter that data while the other application can alter the replicated data on the BCV volume. Each change occurs with respect to a track or other data block. During these operations, the location, or track, of each change is also identified.
When it is desired to update the data on the BCV volume with the data on the standard device, one of two methods are used. In a first, the ESTABLISH command causes all the data in the standard device to be copied to the BCV volume. The second method is more efficient. A RE-ESTABLISH command identifies all the locations or tracks on which data was changed in the standard and BCV volumes since a previous SPLIT operation. The RE-ESTABLISH command then causes only that data to be transferred from the standard device to the BCV device that has been changed on either the standard or BCV volume. As will be apparent, if fewer than 100% of all the tracks are changed, the RE-ESTABLISH method reduces the time for bringing the BCV volume into synchronism with the standard volume.
The use of BCV volumes with various commands as disclosed in the above-identified patent has proved to be a very powerful tool for data processing. It provides individuals with flexibility in the handling of data and, by virtue of the ability to replicate data with minimum interference to normal operations, increases the reliability of the overall data processing system. Recently, however, new requirements have emerged that make it highly desirable to replicate data onto multiple BCV volumes with repeated updates of the replicated data.
The presently available system is constrained. If two BCV volumes are established and split, the RE-ESTABLISH command can only be used to connection with the most recently defined STANDARD-BCV device pair. This constraint is imposed because changes in the standard device are not maintained separately for each BCV device. Otherwise the REESTABLISH command is rejected. Assume for example it was desired to establish a STANDARD-BCV pair for a first BCV volume (i.e., a standard STD-BCV(1) pair), to split that pair, establish an STD-BCV(2) pair, split that pair, and then update the BCV(1) volume. With the prior system it was necessary to process the ESTABLISH command to update the BCV(1) volume.
The time required to transfer all the data in response to such an ESTABLISH command can greatly exceed the time to transfer the data in response to the REESTABLISH command. Therefore, it is highly desirable to provide a method and apparatus that would permit the use of the REESTABLISH command with multiple standard STD-BCV pairs without regard to any foregoing command sequence.
Therefore it is an object of this invention to provide a data storage facility that allows data on a standard device to be replicated to multiple storage devices whereby the data in each copy can be updated on a periodic basis in an efficient manner.
Another object of this invention is to provide a data storage facility that allows data on a standard device to be replicated to multiple storage devices and that enables copies to be updated by transferring from the standard device only that data necessary to reflect the changes that occurred to the data in the standard and copied other storage device.
Yet another object of this invention to provide a data storage facility that allows multiple copying of data from a standard device and the updating of those copies efficiently and transparently to any interaction between a host device and the data in the standard device.
In accordance with one aspect of this invention, a data storage facility comprises first, second and third data stores that interact individually with first, second and third programs respectively. Each of the second and third data stores can be selectively connected as mirrors for the first data store at different times. Each of the second and third data stores can also be detached or split from the first data store at different times whereupon they are enabled to interact with the second and third programs respectively. When it is desired to update the data in one of the second and third data stores, it is re-established as a mirror, but only the data that has changed in the corresponding second or third data store and the data that has changed in the first data store are transferred.
In accordance with another aspect of this invention, a data processing system has a first application program adapted to interact with data in a first storage device located on the first physical disk storage unit. At least two additional programs can be enabled to interact concurrently and independently with copies of that same data. Specifically, the system identifies additional storage devices on different physical disk storage units for each of the additional programs. A session reference for each of the additional storage devices has entries for recording each change made to a corresponding portion of the data on the first storage device. A device reference is also established for the first and each additional storage device with entries for recording each change a respective programs makes to a data portion on the corresponding storage device. Independent copies are generated for transfer to the other storage devices and for use by their respective additional programs. Each time a program makes a change in a data portion, that event is recorded in the device change reference associated with the program and data storage device while the systems are operating independently. On demand updating of a copy occurs with a selected storage device by combining the entries in the corresponding session and device change references to identify changed data portions and to control the data that is transferred from the first storage device to the selected storage device.
In accordance with another aspect of this invention, a multiprocessor data processing system includes a data storage facility wherein one program operates with data in one data storage device and a plurality of other programs wherein each other program interacts with another data storage device. Multiple copies of the data from the one storage device are made on each of the additional data storage devices for operation with their corresponding programs. The interaction between these devices includes defining a first buffer for each additional storage device on which a copy is to be made and a second buffer for each additional storage device and the one storage device. Data from the one storage device is copied to one of the additional data storage devices thereby to enable another program to interact with the data copy on the additional data storage device independently of the data and of the program being utilized with the one data storage device. Each change made by the one program to data on the one storage device and by the other program to the corresponding additional storage device is recorded in the first and second buffers respectively. Upon completion of independent operation, the information in the corresponding first and second buffers can be combined to identify data to be copied from the one data storage device to one additional storage device thereby to enable the data to be copied so the data in the additional storage device replicates the data in the one data storage device.